I have a stock '86 Firebird with stock everything.(305, tranny, rear end, etc.) I just recently bought an aluminum drive shaft from a '91 GTA that I'm going to put in my car and am also building up a stoughter engine, making around 350-400 horse. I plan on upgrading my tranny, but am now wondering about my rear-end. It's got 3.08 gears in it, and I want to swap to around 3.40. I believe I have a 10 bolt and am wondering what gears I CAN swap to and even if my rear-end will be able to handle that power. I want to make it a posi also. So would I be better off finding a new rear-end that comes like wanting I'm wanting, posi, 3.40's etc. or should I have someone re-do mine to those spec.'s? Thanks! Also if this is the wrong forum to put this under I apologize, but this is as close as I saw for rear-ends.

 

i'd look at an aftermarket posi and 28 spline axles and have them installed in your rear, or find a posi rear from a 90 and later f body, all depending on cost. you can get gear sets in about anything you might want up to 4:56s.

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Now would that require me getting an entire new rear end if I went the after market way, or would I just have to replace the internals and axles? Also, what options did the '90 up F-bodies come in as far as the rear end is concerned. Gear ratio, posi's, etc. Thanks for the insight!

 

I would go with the aftermarket axles and posi and gears. If you go aftermarket, that is all you have to change. As for the stock options of 90-Up the z28's and formulas(i think) and trans ams came with posi, and no better than 3.08 gears as you have, in 88 or 89 they started putting in 28 spline axles stock. I think most of the aftermarket posi units you will find utilize the 28 spline axles, so that is why you need to upgrade, plus they are stronger.

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90 and up gear ratios are 2.73, 3.08, 3.23, or 3.42, depending on engine and options. 90 and up is when you'll see almost all rearends are 28 spline ten-bolts.

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So if I could snag me a 3.42 posi, from a newer 3-gen. i'd be set then...